Homework 2, Math 320, Spring 2001

Name:____________________________      Section number:______

## Math 320 Homework #2 --- Due 2/2

Include your name, section number, and homework number on every page that you hand in. Enter ``Section 1'' for the morning class (10-11AM) and ``Section 2'' for Professor Sawyer's class (12-1PM).

You can begin the exposition of your work on this page. If more room is needed, continue on sheets of paper of exactly the same size (8.5 x 11 inches), lined or not as you wish, but not torn from a spiral notebook. You should do your initial work and calculations on a separate sheet of paper before you write up the results to hand in.

Output from Excel must have your name, Section number, and the homework number in cell A1. Staple all sheets together. No unstapled papers will be accepted.

1. Plot by hand on graph paper or plain white paper the e.d.f. (empirical distribution function; see Section 2.3) for the accident-by-week data given in Exercise 2.12 page 47. (Hint: Construct a dot plot first.) Refer to the dot plot or e.d.f. to answer the following questions:

1. What percentage of the weeks had fewer than 5 accidents?
2. What percentage of the weeks had fewer than 10 accidents?
3. What is the median of the data? (Hint: For n=50 observations, the median is the average of the 25th and 26th observations, counting from either the bottom or top of the observations.)
4. Find the mode of the values.

2. Find the sample mean Xbar and the sample standard deviation Sx of the data in the previous problem. (Hint: It may be useful to use a calculator or Excel. Click here for some notes about using a calculator or Excel to do statistical calculations.)

3. Use Excel to do Exercise 2.32 on page 59, which first asks you to construct a scatterplot. Excel calls a scatterplot an XY(Scatter) chart. Here are some hints. Open a new workbook or go to a fresh sheet. Don't forget to enter your name and homework number in cell A1. Enter ``Percentages'' in cell A2, ``Over 65'' in cell A3, and ``Nonwhite'' in cell B3. Highlight the three cells and use the ``B'' button on the menubar to put the three cells in boldface. Enter the numerical data underneath the column headings in columns A and B beginning with cell A4.

Click on cell A3 and drag to highlight the whole block of data, including the labels. Click on the ChartWizard icon (the sixth or seventh icon from the right on the icon bar, which looks like a vertical bar chart with three vertical bars of various colors.) Follow the steps the ChartWizard leads you through. At the appropriate step, enter ``Counties in Florida'' as the Chart title, ``Percentage over 65'' for the X axis, and ``Percentage nonwhite'' for the Y axis.
Answer the two questions posed in the problem. Write in complete sentences. Make your interpretation of the data clear to the reader of your paper.

4. Do Exercise 3.16 page 91. Use a calculator to compute both the means and standard deviations of the two samples of ten mice. (Recall that you will be able to use a calculator to do problems on tests, but not Excel.)

5. Do Exercise 4.16 on page 137 in the text. Indicate briefly how you arrived at your answer to each part.